Since Mr. R. B. Merrifield disclosed the theory of solid phase peptide synthesis, various resins for synthesizing peptide have been developed.
Chloromethyl polystyrene resin disclosed by Merrifield is important as the first resin used for solid phase peptide synthesis. However, chloromethyl polystyrene resin has been applied to very limited cases of solid phase peptide syntheses because strong acid such as hydrofluoric acid(HF) are required to recover synthesized peptides.
Therefore, Wang resin having a structure of 4-alkoxybenzyl alcohols has been developed in order to overcome the drawback of chloromethyl polystyrene resin.
Wang resin has been widely employed in solid phase peptide syntheses because it allows synthesized peptide to be recovered under more weak acid conditions than chloromethyl polystyrene resin.
However, Wang resin is not suitable to be used in obtaining peptide products with their protecting groups retained, because the protecting groups combined on their side chains are eliminated during the separation process of synthesized peptides from Wang resin.
In addition, Wang resin has the drawbacks that catalyst for activating alcohol group is required to combine a first amino acid to resin, that racemization may be appeared or that diketopiperazine may be formed.
Therefore, tritylated polystyrene resin of the present invention has been developed in order to overcome the above drawbacks of Merrifield resin and Wang resin.
Peptides can be separated from solid phase under weak acid condition by using tritylated polystyrene resin, so that the protecting groups combined on their side chains can be retained during the separation.
In addition, catalysts are not required to introduce a first amino acid on the substrate resin because the chemical structure of trityl group is activated in itself. Furthermore, the formation of diketopiperazine and racemization can be advantageously suppressed during peptide synthesis process because trityl group causes great steric hindrance effect.
Meanwhile, trityl group can be introduced to polystyrene resin by introducing linkers having trityl group to the resin after the preparation of the polystyrene resin, or by polymerizing styrene monomers having trityl group.
J. M. J. Frechet et al. disclosed a process introducing bezophenone group on polystyrene resin by using benzoyl chloride and then, synthesizing tritylated polystyrene resin by using Grignard reagent(Tetrahedron Letters No.35, pp3055-3056, 1975).
U.S. Pat. No.5,922,890 disclosed a process for preparing tritylated resin wherein dichlorobenzo phenone is reacted with 4-tolylmagnesium bromide, and oxidized to give 4-(bis-(4-chlorophenyl)-hydroxymethyl)benzoic acid, and then 4-(bis-(4-chlorophenyl)-hydroxymethyl)benzoic acid thus obtained is combined to resin having amino group to give the tritylated resin.
G. Orosz has developed a process for preparing 2-chlorotrityl polystyrene resin in which 2-chlorobenzophenone group is introduced to the benzene moiety of polystyrene by reacting the polystyrene with 2-chlorobenzoyl chloride and then the resulted product is reacted with phenyl lithium to give 2-chlorotrityl polystyrene resin(Tetrahedron Letters No.39, pp3241-3242, 1998).
However, the processes described in the above require hard reaction conditions and enormous manufacturing cost because all of them employ strong basic Grignard reagents or highly reactive organo metallic compounds.
Especially, the above process for preparing tritylated resin requires the use of organo metallic compounds, which are hard to handle during large-scale process. Also, this process is too long and complicated so that the production cost can not but increase.
Therefore, a process for preparing tritylated polystyrene resin used for synthesizing peptides, which does not require the use of organo metallic compounds and not require complicated steps, has been anticipated in this field for a long time.